Project 2 (SPECT) will examine single photon emission computed tomography (SPECT) data in two cohorts of subjects, in order to identify early predictive factors for the development of Alzheimer's disease (AD). The first group of subjects (Cohort 1) consists of those individuals recruited and followed during the last funding cycle (n=165). A second sample (Cohort 2) will be recruited during the next funding cycle (n=106). Both cohorts consist of controls (CDR=0) and subjects with "questionable" AD (CDR=0.05). Project 2 will gather data on these participants in order to identify SPECT variables that predict which subjects will later progress to the point where they meet criteria for AD. Data from Project 2 will also be combined with data from other projects and Cores to determine the variables from all of the major domains of interest (e.e., neuropsychology, SPECT, fMR, genetics, etc) that best predict the development of AD.